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  1. #1
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    My comically inadequate heating

    Felt the desire to share with the board, how comically inadequate is the forced air ductwork in my house, in winter heating mode. Currently with a cold (for S.Texas) night, am seeing 7 degrees difference between temperature at the thermostat, and temperature in the master bedroom and bath(!). Thankfully it is the master bath which is the warmer location.

    At present I think the system airflow is reasonably close to optimum in cooling mode, but the heat loss per room is very different in winter. My room by room Manual J calc shows the heating load is distributed differently than cooling load. Therefore there is no one solution for airflow in both modes, just a compromise. I do believe what I am seeing also tells me actual heating loads are kinda different from the Manual J model.

    Overall there is enough heating capacity with two-stage Trane gas furnaces, it just has trouble getting distributed to the right rooms. I don't have much hope that this can be completely fixed without having special ducts for heating vs. cooling, or thermostats in the problem areas controlling some kind of local heating. I may be a nut but not nutty enough to do a Rube Goldberg thing here. If anyone here has suggestions then I am eager to hear them and try to implement them, but the way our S.Texas winters go the winter will be gone before too many things can be tried. I am trying little things like running the (VS) air handler continuously for parts of the day.

    Way back in 2003 I had noticed one bedroom being a few degrees colder, that got me started on this whole odyssey of trying to learn what a consumer might need to know about HVAC. Tried to employ some professionals in this case, with little results. Cannot blame them for lack of expertise in winter problems, not in a cooling dominated climate like S.Texas. Too much of a niche problem for them.

    As long as the whole system works in the long summer, I can grin and bear its shortcomings our rather short winter.

    Best wishes all -- Pstu

    [Edited by pstu on 12-02-2006 at 10:15 PM]

  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,011
    Only cheap fix I know of would be manual dampers, or if your rich and lazy get an auto damper system installed, or if your really rich get you one of them there Carrier Infinity systems installed, or because I sell RUUD I would get me a RUUD Mod. zoned system installed, lots of choices here.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  3. #3
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    you seem to be experiencing an anomaly or a down right paradox.


    We serve a norther clime so the design criteria is a lot different, but one thing remains constant: If you can cool the house then you can reasonably assume that it should heat.
    The requirements for cooling duct systems are such that their size must be larger than heating only systems.
    So saying, larger duct size should allow the heating system to work.

    You may have to balance the system for winter operation VS summer cooling.

    If you have ceiling diffusers it makes a big diff too (northern climes use floor registers).

    If there are two or three outside walls to the rooms in question, then welcome to my world. They will be the coldest rooms in the home.

    Is the furnace kickin into high fire? How is the insulation in the home?

    Is the furnace right sized?

    Location of stat?

    Now this is what I would draw as a first assumption without being there.

    I think you should holler for one of the Texans who frequent this board. They can help you better than this Yankee.






  4. #4
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    2,016
    I'm not sure if I'm reading that you have a two stage furnace or not, but if you do the problem you're describing is common when the ductwork is not sized properly. In your part of the country air conditioning is the prime consideration in sizing leading to larger ductwork than you need for full heating. Now add a two stage furnace that delivers even less air flow during 1st stage heating and the longer runs suffer.
    One thing you can try is running the blower on continuous for a couple of days to see if this helps the problem. If it does, then this could be one solution.
    You could try a zoning system, but this adds it's own problems with both heating and cooling.
    If you have access to all of your ductwork you might look to see if there are dampers installed in the runs to every register. By experimenting you might find the right balance to make your system work in the winter months. If you've done the heating and cooling loads you can take your answers for each room for cooling and heating and assign percentages to each room and use this as a basis for adjustments of the dampers for each season.
    Limiting air flow to any equipment can cause damage. I strongly suggest that you keep looking for a company that does system balancing.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  5. #5
    Join Date
    Jan 2005
    Posts
    84
    I had a similar problem in a couple of rooms during these Texas cold snaps:, although the delta between t-stat and actual room temp was about 4-5 degrees. After upgrading the old single-paned windows and attic insulation the delta is rarely more than one degree. The greater benefit of the windows is realized during the summer. T-stat and actual temp is usually the same. I have a hunch that once we replace the rest of the windows my hvac systems will be oversized. I realize your rooms may not have as much glass area as the rooms I was dealing with. And it's not the cheapest fix up front. One option might be to employ a portable electric heater. We have a Honeywell model about 4 foot long that works great keeping our babies' room toasty. Its a digital model with a timer that cost a whopping 40 bucks at Depot. It might be the cheapest alternative considering the brevity of your winters.

  6. #6
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    Many clues, answers well concealed

    This 1989 house is built with good craftsmanship and design in some ways, but good design in Texas HVAC is rarely seen. Insulation is good enough IMO, fiberglass batts cut to fit the many odd shapes in the ceiling (architect got a little creative here). The furnace is a two-stage Trane, and running continuous fan does seem to help some. Furnace is 64K BTU output vs. Manual J requirement of 46K, smallest available with a Trane 4-ton VS air handler. Long runtimes on 1st stage, with 2nd stage rarely seen except when stat (Totaline 1700) setpoint is 3 or more degrees above current room temperature.

    Ductwork appears generously sized, I am no Manual D whiz but the sum of supply ducts is about 400 sqin. It probably was installed with little knowledge of ACCA (Manual D) methods. There have been dampers added at the plenum for each supply trunk. I *have* been experimenting with clamping down airflow to the overheated rooms, also have been watching ESP and it is not dangerous.

    Supply vents are ceiling mounted, and high ceilings are indeed challenging in the winter. Many rooms have ceiling fans which can reduce temperature stratification. My room by room Manual J reports master bedroom heating load 17.7% of the total, cooling load 19.7%. For the bathroom suite, 14.0% of the heating load, 17.1% of the cooling load.

    That tells me the duct system should be designed for the higher airflow, which means unless dampers are reset for the winter it will be overheated by design. To compound the situation, the original HVAC installer gave each bathroom much more airflow than heating or cooling requires.

    The final challenge in this house is a thermostat mounted on a wall which is partially exposed to the attic. I recently heard a building pro refer to a condition called "hot wall" which I strongly suspect describes this wall. During cold spells its temperature is more like an exterior wall than an interior one.

    Without designing some serious changes in the duct system, it appears more productive to buy a local electric heater and try to laugh at these foibles. I will try to solve them but won't put out the same effort as for a summer cooling problem. Our climate is hot-humid, winter design temperature is 32F, and winter will be over before I could coordinate much of anything with contractors.

    Thanks for listening! -- Pstu

  7. #7
    Join Date
    Jul 2005
    Posts
    717
    Pstu has given a lot of information???.... except the main one... WHAT IS THE TOTAl SQUARE FOOTAGE OF THIS HOME, and perhaps if we also knew the sizes (L xW and ceiling heigths) of these 'hard to heat rooms' and what size of supply and return serves them, it would be very beneficial in giving a proper answer to these problems.

  8. #8
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I don't want Deejoe to think I am stiffing his question... this is a 1600 sqft wing of a two-wing house (to simplify I had only described one of two systems). The rooms actually hard to heat are connected in an open fashion:

    Dining room 200 sqft, 14 ft ceiling, supply one 7-inch and one 6-inch duct
    Den 420 sqft, 12 ft ceiling, supply two 7-inch ducts

    There are two returns adjacent to these rooms, one ceiling mounted and one built into that wall which seems to be relatively exposed to the attic temperature (some insulation but acts like an exterior wall). Each return is 18 inches, all ducts are flex.

    Wouldn't you rather watch football on a Sunday rather than get too deep into this quagmire of a problem? If you really have an insatiable desire for numbers I could email a PDF file detail report made by Hvac-Calc. Pretty sure a key factor is heat loss in winter is high compared to heat gain in summer, and the ductwork tries to serve summer and is hit-and-miss for winter.

    Again I am not asking for answers here unless something just seems obvious to you. As long as heat gain is stronger in some rooms than heat loss, these problems will persist.

    Best wishes -- Pstu

    P.S. It was pointed out to me the smaller duct ought to be on the smaller room, that was a typo by me.


    [Edited by pstu on 12-03-2006 at 06:25 PM]

  9. #9
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,011
    I am no A/C or Heating wizard but I get by , but my cup is overflowing with good old common sense and experience, my guess would be that if you are having a problem either heating or cooling any room in a home your have a couple choices, move more air into that room or area by adjusting dampers if you have those, or do something do help the air in that room or area to retain the heat or cold that is dumped into there, that being windows, tint, insulation, etc. this is just a good old Country boy common sense guess.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  10. #10
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,584
    Den 420 sqft, 14 ft ceiling, supply one 7-inch and one 6-inch duct= max/130cfm (7") max/100cfm (6")
    Dining room 200 sqft, 12 ft ceiling, supply two 7-inch ducts
    (7")130cfm
    (7")130cfm

    Looks like you have some issues with duct layout, with larger sizes were smaller are needed . Need to have dampers on all supplys at VS furnace and maybe increase airflow with dip-switches.

    And do you have (2) stage thermosat?
    If not I would recommend you get one with remote sensor to bedroom so you can take average from both areas and set thermostat to maintain temperatures.

    INVESYS 9720i
    with remote sensor.
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  11. #11
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    My error on duct sizing

    I am hearing some sound advice here. Gotta say that was a goof of mine about the smaller duct being on the larger room, entirely my mistake typing. It is corrected on the original post now, it is actually the den which has the larger ducts. That den probably still wants more, as there is a large bank of windows on one wall. My Manual J calc says it has 37% of the heating load and 28% of the cooling load, yet it squeaks by with only 23% of the airflow. It seems to be OK in the summer though, that surely seems to be a paradox.

    Gosh. When the master bedroom and bath are comfortable temperatures in winter, the big empty areas in the house are not. We hardly ever use that dining room, my main concern with the den is the thermostat is located there. That thermostat is a two-stage Totaline 1700, but I sure wouldn't mind having it in a different location.

    Again I must say that on this winter problem I am going to be more talk than action. Although it sounds nice to replace the thermostat with a pair of others, I may be real slow to actually do that. My gracious wife points out that it is keeping her comfortable, so any fine tuning is academic this time<g>.

    Thanks for listening, and thanks for sharing your ideas!
    -- Pstu

    [Edited by pstu on 12-03-2006 at 08:00 PM]

  12. #12
    Join Date
    Jul 2005
    Posts
    717
    One of the first to do would be to block off that ceiling return,because it's just taking all the HEAT back out of the room. It's better to have LOW to the floor locations for RETURNin the winter months.
    That ceiling return is fine for the Summer cooling months but NOT for the Winter heating months.

  13. #13
    Join Date
    Apr 2002
    Posts
    11,808
    pstu, maybe reverse the rotation on any ceiling fans in those high ceiling areas.

    It causes air to move up to the fan and then hit the ceiling and move towards the walls. It pushes warm stratified air towards the walls and then forces it down the walls to the floor level.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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